Question

I have an application that will generate reports from various databases, each with the same schema. The only difference between DB1, DB2, DB3, and DBx is the data. All tables, views, etc are the same in structure.

For each participating DB in my application I have created a distinct Linq to SQL DataContext.

I am creating a ReportHelper class that will generate reports from the underlying data. I want to be able to call a Method like “GetCustomerSales” and have it spit back the data for my report. The problem is that I want to pass or set the DataContext for the GetCustomerSales method before I call it (ideally when constructing the ReportHelper Class).

However, my GetCustomerSales method wants me to use a specific DataContext, and I do not want to create this method over and over for each potential DataContext in use in the app. What’s the correct approach here?

Answer 1

Have a single data-context, that matches the common schema. The difference is that instead of using just new SomeDataContext(), you should supply an appropriate connection-string (or connection) to the constructor:

var db = new SomeDataContext(connectionString);

or

var db = new SomeDataContext(connection);

Now all you need is multiple connection-strings, which is easier than multiple data-contexts. Two choices there; you can store multiple strings, perhaps in config (this is especially useful if they each need different user accounts etc); or – you can use SqlConnectionStringBuilder to create the connection string at runtime, specifying the appropriate database.

To illustrate; every site in the StackExchange network is ultimately a different database, but they all use the same data-context type. We simply tell it about the connection at runtime (based on which hostname you accessed).